The present invention relates generally to a hinge assembly for rotatably coupling a first member to a second member and, more particularly, to a hinge assembly having a pre-loadable friction element which controls and influences the angular position of the first member with respect to the second member.
It is often necessary to control the angular position of a first member which is rotatably coupled to a second member by a hinge. Such control is often economically and efficiently provided by employing one or more friction hinges. Friction hinges are well known and are disclosed in U.S. Pat. Nos. 5,491,874 and 5,752,293, which are incorporated herein by reference. Friction hinges are particularly well suited for xe2x80x9cclamshellxe2x80x9d devices such as laptop or notebook computers, personal digital assistants, and other hand-held devices having a similar two-part configuration where a cover or display screen rotates relative to a keyboard or the like. Friction hinges permit a user to position the display screen or cover relative to the keyboard, cover, etc. and maintain the relative rotational position of the two parts. In a laptop computer, for example, the display screen rotates from a closed position wherein the screen is in face-to-face mating engagement with the keyboard to an open position where the display screen is positioned generally within a range from about perpendicular to the keyboard to approximately one hundred thirty-five degrees with respect to the keyboard. In such a configuration the friction element of the hinge is normally structurally fastened to the base of the computer and the shaft is connected to the display screen. When the display screen is rotated about the axis created by the hinges, it is held in a desired angular position by the force generated between the friction element(s) or member and the pintle or shaft.
Many other applications exist for such friction hinges. For example, in many automobiles of recent vintage a pivotable display screen is provided for viewing of pre-recorded video or for display of video games. Such display screens are often interior roof-mounted and rotate from a closed position wherein the display screen is generally parallel to the roof of the vehicle to an open position directed toward the viewer. Due to the variety of sizes of viewers and positions for viewing within the automobile it is often necessary to change the angle of the display screen with respect to a closed position. In such applications, friction hinges provide an inexpensive and convenient mechanism for maintaining the display screen in a desired orientation.
One drawback to standard friction hinges is that, in a given direction of rotation, such hinges apply generally uniform resisting force throughout their rotational range to movement of the first and second members relatively to one another. Thus, uniform resistive force is applied to each by the hinge from the closed position to the full open position and vice-versa. The result of this, when one considers the closed position, is that the user must exert significant force to separate the two halves of the device. In other words, once a retaining catch or similar retention feature that maintains the two halves of the clamshell-type device in a closed position is released, the user must engage one or more fingers on what is usually a very small gripping feature and separate the two halves of the device against a significant resistive force applied by the friction hinge. This act can be difficult due to the resistance to rotation built into the friction hinge and also due to the force of gravity where a cover or display panel must be rotated upwardly with respect to the lower half of the device, such as in a laptop or notebook computer. The hinge assembly of the present invention provides an initial lift or xe2x80x9cpop-upxe2x80x9d from the closed position to facilitate opening the clamshell device.
Another drawback to prior art friction hinge designs is that the resistance to rotation provided by the interaction between the friction member and the pintle or shaft differs, depending on the rotational direction of the friction member with respect to the pintle or shaft. When the pintle rotates in a direction counter to the direction of wrap of the friction member around the pintle, the resistive force is lower than when the pintle rotates in the opposite direction with respect to the friction member. When a prior art friction hinge assembly is installed in, for example, a laptop computer, the hinge assembly is configured such that the lesser resistive force is encountered when moving the display portion and keyboard portion toward the closed position and the greater resistive force is encountered when moving the display portion and keyboard portion toward the open position. In configuring the hinge assembly for such a device, the resistive force is predefined so as to prevent the display portion from moving toward a closed position with respect to the keyboard portion solely from the force of gravity. The drawback to this configuration is that when the keyboard portion of the laptop is resting on a desktop, the increased resistive force encountered in moving the display portion from the closed position to the open position may cause the keyboard to lift off the desktop due to the relatively greater resistive force encountered in opening the device. Given the respective weights of the display and keyboard portions of current laptop computer designs, it is desirable to have a hinge assembly that provides not only the initial lift described above, but also equal resistance to rotation in both directions so as to eliminate lifting the keyboard portion off the desktop when moving the display portion from a closed position to an open position with respect to the keyboard portion.
The present invention overcomes many of the disadvantages inherent in the conventional friction hinge assembly by providing a friction hinge that gives the designer the option of creating equal resistive forces in both rotational directions. The present invention also overcomes such disadvantages by providing a pre-load that assists in urging the friction element and pintle or shaft from a predetermined angular position so as to, for example, assist in separating the halves of a clamshell-type device.
A hinge assembly for rotatably coupling a first member to a second member. A pintle is secured to the second member and includes a cylindrical external surface having a first longitudinal portion and a second longitudinal portion. A friction element is secured to the first member and includes a first cylindrical wall wrapping at least substantially circumferentially around the first longitudinal portion of the pintle in a first circumferential direction. The first cylindrical wall is configured to provide an interference fit with the pintle such that the first cylindrical wall applies a first generally radially directed compressive force to the pintle. The friction element further includes a second cylindrical wall wrapping at least substantially circumferentially around the second longitudinal portion of the pintle in a second circumferential direction. The second circumferential direction is opposed to the first circumferential direction. The second cylindrical wall is configured to provide an interference fit with the pintle such that the second cylindrical wall applies a second generally radially directed compressive force to the pintle.